This invention concerns a method of measuring the parameters of fresh water and waste water and an analysis device for measuring them.
Especially with automatic analysis devices, besides the constant availability of measurement, the consumption of chemicals is increasingly coming to the fore, which has a major influence on the cost of operating the device. The devices that work discontinuously that are on the market reduce the consumption of chemicals by increasing the measurement interval. But this drastically reduces the availability of the measured values. Thus, peaks or quick short-term fluctuations are lost by the measurement technology. Controlling a sewage-treatment plant after short-term fluctuations like cloudbursts, is therefore no longer possible.
The problem of this invention is to create a measurement method and an analysis device that minimize the consumption of reagents and chemicals, without losing information relevant for measurement technology.
The present invention provides a method of measuring parameters of fresh and waste water, comprising: determining a time change or first derivative of measured values from the measured values of at least two successive measurements, by dividing a difference between the successive measurements by a value corresponding to a time interval of the measurements; determining a pause interval until a next measurement, depending on a value of the time change or first derivative; comparing the value obtained for the time change in the measured value or first derivative with an allocation function, which allocates a correlating pause interval to the value; varying a length of a basic interval varies depending the value of the first derivative; and setting the basic interval manually or by program control according to the time of day or time progression within a period of time.
Also, the present invention provides an analysis device for parameters of fresh and waste water, with a control unit and at least one measurement arrangement for measuring a parameter of fresh or waste water, wherein the measurement is taken at time intervals, and the device comprises: a differential circuit for finding a differential value from a difference between successive measured values; a comparative circuit for comparing the differential value obtained with an allocation function filed in a reference-value storage unit and allocating an interval value obtained from the allocation function to a time-measurement component, whereby a measurement cycle can be initiated; and an interval changing circuit for changing the interval between measurements depending on the time, wherein the differential circuit divides the difference between successive measurements by a value corresponding to the time interval of the measurements and sends the differentiated value as the different value to the comparative circuit.
According to the invention, the difference between the values measured in two successive measurements is divided by a value corresponding to the time between the two measurements. This gives a first derivative of the measured value according to the time. If the value of this derivative is higher, this means that the measured values have changed a great deal compared to the last measurement. In this case, a shorter interval is used until the next measurement. If the value is lower than the first derivative, this means that the measured values have not changed very much, so the pause interval can be set to a higher value. This way, it is possible to adjust the measurement interval to the change in measured values. For example, if faster or shorter fluctuations occur, this results in a clear increase in the first derivative of the measured values, and then shorter measurement intervals can then automatically be set accordingly, until the short-term change is gone and the first derivative assumes smaller values again. If the changes in the measured values are only very slight, a very long pause interval can be set.
Thus it is possible to minimize the consumption of power and chemicals for measurement, without losing information relevant for measurement technology.
Preferably, an allocation function, for example in the form of a table or a mathematical function, is stored in the measurement device, and a certain value of a derivative can be assigned right away to a certain pause interval. This method of control is very simple to use with no big hardware or software expense.
A device for analyzing the method requires a differential circuit that finds the difference between successive measurements and divides that difference by a value that corresponds to the time interval between the measurements. A comparative circuit must also be provided in order to compare the value obtained in the first derivative with corresponding values of an allocation function and from that function to obtain a pause interval to set the time for the next measurement.
Of course, manual adjustment can be provided in order to influence the measurement intervals set automatically in the way described above, for example to reduce or increase them.
The first derivative of the measured value is expressed as dC/dT, where C is the concentration measured for one parameter of fresh or waste water and T is the time between the two measurements. Of course, the last two measurements need not be used to calculate the first derivative. The derivative can also be calculated from several measuring points or it is also possible not to use the last two measurements to get the first derivative. This can vary depending on the individual requirements. The measurement method can especially be used for a phosphate assay in an activator basin.
Of course, the method can be lengthened or shortened by a basic interval depending on the value of the first derivative. It is now possible to input the basic interval variably, for example for different days or times of the day, in order to influence the measurement process thereby as well. This change in the basic interval can also be program-controlled, i.e., can be made automatically. The basic interval is then generally set shorter in times when greater fluctuations occur in the waste water or can be expected in the type of waste-water occurrence.